Automatic reclosing circuit interrupter



Oct. 3, 1950 B. R. HERMANN ETAL AUTGMATIC RECLOSING CIRCUIT INTERRUPTERFiled Nov. 5, 1945 lvm/enters: Berg' @mim IQ. H erm am rw,

Sidney F2. Smithr,

by A

Their/@torn ey.

Patented Oct. 3, 1950 AUTOMATIC RECLOSING CIRCUIT INTEREUPTER BenjaminR. Hermann, Lanesborough, and Sidney R. Smith, Jr., Pittsfield, Mass.,assignors to General Electric Company, a corporation of N ew YorkApplication November 5, 1945, Serial No. 626,840

9 Claims. l

Our invention relates to automatic reclosing circuit interrupters andmore speciically is an improvement on the invention disclosed andclaimed in copending Lincks and Jensen application, Serial No. 468,522,filed December l0, 1942, now Patent No. 2,414,786, granted January 2l,1947, and assigned to the same assignee as the present application.

Automatic reclosing circuit interrupters have in recent years beenextensively used in distribution systems. Such automatic reclosingcircuit interrupters are employed in such distribution systems andcoordinated with fuses and the like so that in the event of a fault onthe system whether the fault is permanent or temporary in nature, therewill be a minimum of service discontinuity. Along these lines adistribution system is sectionalized at many points and if the fault isof a permanent nature it is desirable that only the small section wherethe fault is located be disconnected from the system and all theremaining portions thereof remain in service.

Automatic reclosing circuit breakers inherently are ideal devices fortaking care of temporary faults since by opening and reclosing one ormore times with substantially no visible inconvenience to customers ofpower service, the fault is disposed of and continuity of servicemaintained. As has been brought out in the above mentioned Lincks andJensen application, continuity of service can be improved particularlywith regard to permanent faults if following several immediatelysuccessive operations of the automatic reclosing circuit interruptingdevice which indicates a permanent fault on the system, thecircuitinterrupting device is eifectively maintained in the closedposition for a short period of time so that protective devices such asfuses controlling the faulted section of the system have time to operateto isolate this faultcd section. Our invention is specifically concernedwith a rather simple arrangement for effectively maintaining theautomatic reclosing circuit interrupting device in the closed positionfollowing successive operations thereof which indicate a permanent faulton the system.

It is an object of our invention to provide a new and improved automaticreclosing circuit interrupter.

It is another object of our invention to provide a new and improvedautomatic reclosing circuit interrupter with simple means foreffectively maintaining the contacts thereof in the closed positionfollowing successive operations which indicate a permanent fault on theassociated syster Still another object of our invention is to provide anautomatic reclosing circuit interruptor of the type employing anelectromagnet for interrupting the circuit in response to an abnormalcurrent condition with simple means for short circuiting saidelectromagnet for a predetermined time following a permanent fault on aportion of an associated distribution system.

Further objects and advantages of our invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize our invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of our invention reference may be had to theaccompanying drawing in which Fig. 1 is a schematic perspective View ofone embodiment of our invention, and Fig. 2 is a schematic diagram of amodification of our invention.

Our invention is particularly applicable to automatic reclosing electriccircuit breakers of the type disclosed in Walle Patent 2,069,082,granted January 2, 1937, and assigned to the same assignee as thepresent application, or reclosing circuit breakers as illustrated in theabove mentioned Lincks and Jensen application. In order to simplify thedescription only the essential portions of such a circuit interruptor inso far as our invention is concerned are shown in the drawing, but itshould be understood that the remaining parts thereof are similar to thedisclosures of the Walle patent or the Lincks and Jensen application.

Referring now to Fig. 1, We have illustrated an automatic reclosingcircuit breaker generally indicated at i which is adapted to beassociated with a distribution system having the line sections 2 and 3connected` thereto. Automatic reclosing circuit breaker l comprises apair of relatively movable contacts illustrated as a stationary contacti and a movable Contact 5 which are respectively connected to thesections 3 and 2 of the distribution circuit with which automaticreclosing circuit interruptor I is associated. Opening of automaticreclosing circuit interrupter l is obtained` through operation. of anelectromagnet having a winding 6 and an armature l. Winding 5 isconnected in series with contacts 4 and 5 and the line sections 2 and 55so that whenever the current increases to a predetermined value due to afault somewhere on the associated system, for example, relativeseparation of contacts d and 5- occurs.

Contact 5 is normally biased to the closed position either by gravityalone or preferably supplemented by means of a spring (not shown).Whenever a fault occurs on the associated distribution circuit contacts4 and 5 are separated to interrupt the circuit. Such interruption of thecircuit causes immediately deenergization of winding 6 and gravitysupplemented by suitable spring means, if desired, causes immediatereclosing of contacts 4 and 5. Thus it is obvious that the serieswinding 6 for operating the circuit interrupter inherently provides thereclosing feature. If the fault is temporary in nature circuit breaker Iwill remain closed after this one opening operation.

As in the Walle patent referred to above, it may be desirable to havethe circuit breaker I open and close a predetermined number of times todetermine whether or not the fault is temporary or permanent. If thecircuit breaker continues to open and close it is evident that apermanent fault exists and it is desirable to isolate that section ofthe distribution system including the permanent fault and only thatsection. As was pointed out above, our invention is specificallyconcerned with an automatic reclosing circuit interrupter in which thecircuit interrupter is effectively maintained in the closed position fora predetermined time upon determining that a permanent fault exists sothat fuses or other circuit protecting devices coordinated therewith mayoperate to isolate the faulty section of the system.

With the arrangement described thus far, circuit interrupter I willcontinue to open and close indefinitely in the event of a permanentfault. As in the above mentioned Walle patent and the Lincks and Jensenapplication referred to above, an operating rod 8 having a ratchetmember 9 attached thereto is associated with movable contact 5 andarmature l. Ratchet member 9 is biased by suitable means (not shown) toengage upon downward movement of contact rod 8 a coactin-g ratchet wheelI2 which is mounted on a shaft II and controls a driving and timingmechanism generally indicated at I2 and also a mechanism generallyindicated at I3 embodying our invention. Every time that circuit breakerI opens and recloses ratchet 9 engages coacting ratchet wheel I androtates it in a clockwise direction as indicated by the arrows in Fig.l.

' In order that relative separation of contacts 4 and 5 may be manuallyobtained contact rod 3 is connected by means of a link I4 to a crank I5rotatable with a shaft I6 suitably mounted in a fixed support. A manuallever Il may be actuated by a suitable switchstick or the like to rotateshaft I5 and consequently open contacts 4 and 5.

As is also disclosed in the above mentioned Lincks Jensen patent, onemeans of effectively maintaining an automatic reclosing circuit breakerof the type disclosed above 1n the closed position is to provide meansfor short circuiting all or a portion oi the series winding 6 of theelectromagnet. Our invention is particularly concerned with a new andimproved arrangement for accomplishing this short circuiting of winding6.

In accordance with our invention, there is mounted on the shaft I Isupporting ratchet wheel Ii) a cam I8 which is generally in the form ofa disk except that it is provided with a raised portion I9. Cam I5 is inengagement with a cam follower 2B pivotally mounted to a xed support allSupported on the end of cam follower 25 is a movable contact 22 which isadapted to engage with a stationary contact 23 when cam follower 20 israised by extension I9 of cam I8. Stationary contact 23 is electricallyconnected to one end of series winding 6 while movable Contact 22 isconnected to the other end of series winding 6 and also to movablecontact 5. With this arrangement, it is obvious that when contact 22 isin engagement with contact 23 series winding 6 is short circuitedthrough these contacts and insufficient current will flow through serieswindn ing E in view of its inherent impedance to cause separation ofinterrupting contacts 4 and 5. As long as contacts 22 and 23, which willhereinafter be referred to as the short circuiting contacts, aremaintained in the closed position, automatic reclosing circuitinterrupter I is effectively main.- taned in the closed position just asmuch as if it were locked in the closed position.

In order to hold short circuiting contacts 22 and 23 in the closedposition once cam i8 has rotated suiciently to close them, we haveprovided a permanent magnet 24 mounted on a support 25 rotatable aboutshaft 2 I. A stop 26 limits the downward movement of support 25 andconsequently the downward movement of permanent magnet 24. The upwardmovement of support 25 and permanent magnet 24 is limited by anotherstop 2l mounted on cam follower 20. Cam follower 25 is provided with amagnetic plate 28 positioned so that, when cam follower 2D is raised bycam I8 to cause closure of short circuiting contacts 22 and 23,permanent magnet 24 will engage magnetic plate 28 and hold the shortcircuiting contacts in the short circuiting position.

In order to reset the automatic reclosing circuit breaker once shortcircuiting contacts 22 and 23 have effectively locked contacts 4 and 5in the closed position, we interconnect the free end of pivotally7mounted support 25 by means of a member 29 and a spring 3G with the endof crank I5, as is indicated at 3l. With this arrangement, it is obviousthat when crank I5 is rotated with shaft I6 upon downward movement ofmanually actuatable lever I'I permanent magnet 24 is moved upwardly awayfrom magnetic plate 28 to such an extent that plat@ 28 is suiiicientlyoutside the range of coercive force of magnet 24 to permit cam follower20 freedom to move downwardly with the consequent opening of shortcircuiting contacts 22 and 23.

When the contact 5 approaches the closed Dosition, support 25 engagesstop 2E. Spring 30 is designed to be entirely slack and does not exertan upward force on support 25 and magnet 24 as the Contact 5 nears itsclosed position. When lever I1 is moved downwardly manually the forceexerted on magnet 24 by spring 3D increases progressively until thespring force is sufficiently great to overcome the magnetic attractionbetween the plate 28 and the magnet 24. The force exerted by the spring30 increases as crank I5 moves counterolockwise due to the increase inthe distance between members 29 and 3l and also because the effectivecomponent of the force exerted by spring 3D is increased due to the factthat the line of action of spring 30 becomes more nearly parallel withthe path of travel of the magnet 24 as the crank I5 is movedcounterclockwise. Thus it will be observed that spring 30 is ineffectiveto move magnet 24 away from plate 28 when the contact 5 is close to orin engagement with the contact 4 and that spring 30 is effective torotate the support 25 when contact occupies a position ,near the upperlimit of its travel.

As the link I4 moves upwardly during automatic circuit openingoperations the magnet 24 moves upwardly obviously without any effect onplate 28 and contact 22 until after the raised portion of cam I8 hasengaged cam follower 20 and caused a predetermined clockwise rotation ofcam follower 20. Since contacts 22 and 23 cannot be closed as a resultof an opening movement of the contact 5, a certain amount of downwardclosing movement of contact 5 is necessary to cause contact 22 to engagecontact 23 during the final one of a series of consecutive reclosures.This downward movement of contact 5 which causes the contact 22 toengage the contact 23 will also result in lowering support 25 and magnet24 into engagement with stop 26 atfwhich position it will perform itsholding function as described above as soon as the contact 22 engagescontact 23. If the spring 30 is not suiiiciently slack at the time thecontacts 22 and 23 become closed to allow the support 25 to engage theplate 26 as might be the case should contacts 22 and 23 close aftercontact 5 had moved only a short distance toward contact 4, then themagnet 24 would be held out of engagement with the plate 28 for a shorttime after contacts 22 and 23 are closed. Further downward motion ofcontact 5 would then lower spring 30, support 25 and magnet 24 and wouldcause a slackening of spring 3u thereby to cause magnet 24 to performits holding function. While the spring 3U is being lowered during thelatter stages of the closing movement of contact 5, the contact 22 wouldbe held in engagement with the contact 23 by the raised portion I9 ofthe cam I8.

It is obvious that once contacts 22 and 23 are closed no furtherautomatic openings of contacts 4 and 5 will occur until after contacts23 and 24 are opened by manually resetting the device by pullingdownwardly on handle Il.

The high speedoperation of an automatic reclosing circuit breaker suchas the one described above causes a certain amount of-vibration, and toprevent this vibration from inadvertently causing bouncing of camfollower 20 so that magnet 24 can hold magnetic plate 28 in its upwardposition, we have found it desirable to provide a second permanentmagnet 32 mounted on a suitable iixed support 33 beneath magnetic plate28 thereby normally holding cam follower 20 in its lowermost positionand also normally holding short circuiting contacts 22 and 23 in theiropen lposition. lt is quite obvious that if cam follower 20 hadsufficient mass, gravity alone would be satisfactory, but for a devicein which cam follower 20 is small and light we have found it desirableto supplement the effect of gravity by means of permanent magnet 32.

By using two permanent magnets such as 24 and 32, it is possible toemploy a stronger permanent magnet 24 than wouldotherwise be the case sothat the contacts would effectively hold in the closed position againstanyr normal vibration. Because of the pull characteristic of magnets,they are much more suitable for this purpose than a spring would be. Aspring would afford a very large pressure to hold cam follower 20 in itsdownward position against the forces of vibration, but unfortunately aspring would constantly apply a pressure to open contacts 22 and 23,whereas magnet 32 will not have this` undesirable effect once magneticplate 28 is moved out of the range of its coercive force.

We have also found it desirable resiliently to support contact 22 fromthe end of cam follower 20. This may be accomplished in any suitablemanner, and we have chosen to illustrate it-in the drawing by means of asemi-resilient plate 34 which is supported by narrow resilient arm 35from the end of cam follower 20. With this arrangement, movable contact22 is effectively mounted on a spring, andas a result bouncing of thesecontacts is eliminated as is also the problem of welding closed of thesecontacts.

It is desirable for an operator to know whether the short circuitingcontacts 22 and 23 are in the closed or open position. To this end, wehave provided an indicator which comprises a plunger 36 movable in aglass cylinder 31 mounted in a visible position on the automaticreclosing circuit interrupter I Plunger 36 is connected by a suitablerod 38 with plate 34 whereupon it clearly indicates by its position inglass tube 31 whether short circuiting contacts 22 and 23 are open orclosed.

The time delay and driving mechanism I2 mentioned above is substantiallyidentical with that described in the Lincks and Jensen applicationreferred to above. The driving portion of mechanism I2 includes a gear39 rotatable with shaft II and a suitable spring 49 which normallybiases gear 39 and ratchet wheel I9 in a counterclockwise direction asviewed in Fig. 1. The time delay portion of the mechanism includes gear4| supported on a shaft 42. Gear 4I is meshed with gear 39. Anescapement device comprising an oscillating member 43 and a cooperatingescapement wheel 44 mounted on shaft 42 controls the speed of rotationof shaft II. Whenever ratchet member 9, having moved upwardly, starts tomove downwardly by virtue of gravity and a suitable spring (not shown),ratchet wheel I0 is rotatedin the direction of the arrows in Fig. l asare also cam I8, gear 39 and shaft I I. Spring 4I) is stressed by thismovement, and oscillating escapement member 43 and associated escapementwheel 44 are actuated. When ratchet member 9 disengages with ratchetwheel I0, spring 4I] returns cam I8 and gear 39 to their initialposition with a predetermined time delay governed by the time delaymechanism specifically co-mprising escapement mechanism 43-44.

In view of the detailed description included above, the operation of theautomatic reclcsing circuit break of our invention will be obvious tothose skilled in the art. When a fault occurs on the associated system,high speed opening of contacts 4 and 5 occurs with a consequentdeenergization of winding 6 and resultant immediate reclosure of thesecontacts. Such opening and closing of contacts 4 and 5, however, causesratchet member 9 to rotate cam I8 a predetermined amount, insuiiicient,however, to close short circuiting contacts 22 and 23. If the fault wasa temporary fault, such opening and closing of contacts 4 and 5 wouldprobably clear the temporary fault and contacts 4 and 5 would remainclosed. Spring would rotate cam I3 to its initial position with apredetermined time delay governed by escapment mechanism i3-44. If thefault is a permanent fault, however, contacts 4 and 5 are openedsuccessively a predetermined number of times until such successiveengagements of ratchet member 3 with ratchet wheel I8 have caused cam I8to rotate sufficiently so that cam follower 20 moves upwardly to closeshort circuiting contacts22 and 22 and 23.

23. When this has occurred, the automatic reclosing circuit interrupterl is effectively maintained in the closed position so that theassociated protective devices, such as fuses and the like, can operateto isolate the permanent fault. The automatic reclosing circuitinterrupter I can be restored to service so it can repeat its protectivefunction by manually operating lever Il. By being maintained in theclosed position, however, continuity of service is maintained and thefault is isolated by suitable associated protective devices into a verysmall section.

It is sometimes desirable to provide an arrangement in which after apredetermined time, such as after the permanent fault has been cleared,the circuit interrupter automatically restores itself so that furtherprotective operations can be preferred without any manual assistancebeing required. Accordingly, in Fig. 2, we have illustrated amodification of our invention in which clearing of the permanent faultcauses the short circuiting contacts to open so that the reclosingcircuit interrupter is restored to its initial condition. Thecorresponding parts of Fig. 2 are designated by the same referencenumerals as in Fig. 1.

Instead of employing a permanent magnet such as 24 in Fig. l, anelectromagnet 45 is provided, which electromagnet A5 has a winding 46connected in series with short circuiting contacts Electromagnet 45 istherefore deenergized when contacts 22 and 23 are open but is energizedas soon as they are closed and consequently eifectively holds camfollower 25) in the upward position as long as it is energized withfault current. Preferably electromagnet 45 is so designed that it isincapable of holding cam follower 2D in its upward position when normalcircuit currents ow but is only capable of holding it in this upwardposition on short circuit currents. Consequently, as soon as thepermanent fault has been cleared by the operation of an associatedprotective device, such as a fuse, electromagnet 45 can no longer holdcam follower 2G in the upward position and short circuiting contacts 22and 23 are opened. In the meantime, spring 4B has caused cam I8 torotate to its initial position so cam follower 23 may move downwardlyand short circuiting contacts 22 and 'Z3 can open.

We have found that our invention is particularly adaptable forconverting automatic reclosing circuit interrupters of the type usedheretofore, which were incapable of being effectivelv "locl:ed in theclosed position when a permanent fault occurred, to this more desirabletype of circuit interrupter disclosed and claimed in the Lincks andJensen application. This conversion can be accomplished with a minimumof change, it being merely necessary to provide the short circuitingcontacts 22 and 23, the magnets and cam follower associated therewith.

It shouldbe understood that our invention is not limited to the speciiicdetails of construction and arrangement thereof herein illustrated andthat changes and modifications may occur to one skilled in the artwithout departing from the spirit of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. An electric circuit interrupting device of the reclosing typecomprising two contacts normally in engagement, an electromagnet havinga winding normally connected so as to be energized by the currentthrough said contacts when they are in engagement and having an armaturewhich directly moves one of said contacts instantly out of engagementwith the other of said contacts when the current through said windingexceeds a predetermined value, means for moving said one of saidcontacts into engagement with said other contact when said winding isdeenergized, means actuated in response to the reclosing movement ofsaid one of said contacts following a predetermined opening movementthereof for completing a short circuit around said electromagnet torender it inoperative to move said one of said contacts out ofengagement with said other contact after said contacts are moved intoengagement by said reclosing movement, magnetic means for effectivelymaintaining said short circuit around said electromagnet, manuallyoperable means for moving said one of said contacts relative to theother, and means responsive to the operation of said manually operablemeans for rendering said magnetic means ineffective to maintain saidshort circuit around said electromagnet.

2. An electric circuit interrupting device of the reclosing typecomprising two contacts normally in engagement, an electromagnetcomprising a winding connected in series with said contacts and arrangedto move one of said contacts out of engagement with the other when thecurrent through said series connected winding and contacts exceeds apredetermined value, means for moving said contacts into engagement whensaid winding is deenergized, means for completing a short circuit aroundsaid electromagnet following a predetermined reclosure of said contactsto render said electromagnet inoperative to move said one contact out ofengagement with said other contact, and magnetic means independent ofsaid electromagnet and responsive to a current through said contacts inexcess of a predetermined value for maintaining said short circuitaround said electromagnet.

3. An electric circuit interrupting device of the reclosing typecomprising two contacts normally in engagement, an electromagnetcomprising a winding connected in series with said contacts and arrangedto move one of said contacts out of engagement with the other when thecurrent through said series connected winding and contacts exceeds apredetermined value, means for moving said contacts into engagement whensaid winding is deenergized, means responsive to a predetermined numberof reclosures of said contacts for completing a shunt circuit around thewinding of said electromagnet, said shunt circuit having substantiallyless impedance than said electromagnet so that the current through saidelectromagnet is insufficient to operate said contact after thecompletion of said shunt circuit, and a second electromagnet responsiveto the current in said shunt circuit for maintaining said shunt circuitcompleted so long as the current therein is above a predetermined value.

4. An electric circuit interrupting device of the reclosing typecomprising two contacts normally in engagement, an electromagnetcomprising a winding connected in series with said contacts and arrangedwith the other when the current through said series connected Windingand contacts exceeds a predetermined value, means for moving saidcontacts into engagement when said winding is deenergized, a camrotatable in response to closing movement of said one contact, a camfollower movable in response to rotation of said cam, a pair of shuntconnected contacts operable to short circuit said winding in response toa predetermined rotation of said cam, magnetic means normally disposedin spaced relation from said cam follower, an armature on said camfollower for cooperating with said magnetic means to maintain said shuntconnected contacts closed after such contacts are closed by said camfollower.

5. An electric circuit interrupting device of the reclosing typecomprising two main contacts normally in engagement, an electromagnetcomprising a Winding connected in series with said contacts and arrangedto move one of said contacts out of engagement with the other when thecurrent through said series connected winding and contacts exceeds apredetermined value, means for moving said contacts into engagement whensaid winding is deenergized, means whereby said main contacts areeffectively maintained in the closed position comprising a circuit inparallel with said winding including a pair of normally open shortcircuiting contacts, means including a cam and cam follower for closingsaid short circuiting contacts in response to a predetermined member ofreclosures of said main contacts, a movable supporting member, a stopmember for holding said supporting member in spaced relation from saidcam follower when said short circuiting contacts are open, and magneticmeans mounted on said supporting member for magnetically holding saidcam follower in the position occupied by said cam follower when saidshort circuiting contacts are closed.

6. An electric circuit interrupting device of the reclosing typecomprising two main contacts normally in engagement, an electromagnetcomprising a winding connected in series with said contacts and arrangedto move one of said contacts out of engagement with the other when thecurrent through said series connected winding and contacts exceeds apredetermined value, means for moving said contacts into engagement whensaid winding is deenergized, means including a circuit in parallel withsaid winding including a pair of normally open short circuitingcontacts, means for bridging said short circuiting contacts to sho-rtcircuit said winding following a predetermined number of reclosures ofsaid main contacts whereby said main contacts are effectively maintainedin the closed position, means including a magnet for holding said shortcircuiting contacts in the closed position once they are closed, a,second magnet for opposing the action of said first magnet, manuallyoperable means for moving said one of said main contacts out ofengagement with the other, and means responsive to the operation of saidmanually operable means for rendering ineffective said holding means forsaid short circuiting contacts.

'7. An electric circuit interrupting device of the reclosing typecomprising two contacts normally in engagement, an electromagnetcomprising a winding connected in series with said contacts and arrangedto move one of said contacts out of engagement with the other of saidcontacts in response to the current through said series connectedwinding and contacts exceeding a predetermined value, means for movingsaid one of said contacts into engagement with said other contact whensaid winding is deenergized, timing means controlled by the movement ofsaid armature for retarding the movement of said one of said contacts,means including a permanent magnet controlled by said timing means inresponse to a predetermined number of actuations thereof for renderingsaid electromagnet inoperative to move said one of said contacts out ofengagement with said other contact in response tc the current thro-ughsaid contacts exceeding said predetermined value, manually operablemeans for moving said one of said contacts out of engagement with theother, and means vresponsive to the operation of said manually operablemeans for rendering said permanent magnet ineffective to render saidelectromagnet inoperative.

8. Anelectric circuit interrupting device of the reclosing ytypecomprising two contacts normally in engagement, an electromagnetcomprising an armature and a winding connected in series with saidcontacts and arranged to move one of said contacts out of engagementwith the other of said contacts in response to the current through saidseries connected winding and contacts exceeding a predetermined value,means for moving said one of said contacts into engagement with saidother contact when said winding is deenergized, timing means controlledby the movement of said armature for retarding the movement of said oneof said contacts, means responsive to a predetermined number ofactuations of said timing means within a predetermined time forcompleting a short circuit around said winding, and a secondelectromagnet responsive to the current in said short circuit formaintaining said short circuit completed as long as the current thereinis above a predetermined value thereby to render said electromagnetinoperable to move said one contact out of engagement with said otherContact.

9. An electric circuit interrupter device of the reclosing typecomprising two main contacts normally in engagement, an electromagnetcomprising a winding connected in series with said contacts and arrangedto move one of said contacts out of engagement with the other When thecurrent through said series connected winding and contacts exceeds apredetermined value, means for moving said contacts into engagement whensaid winding is deenergized, manually operablermeans for moving one ofsaid main contacts out of engagement with the other, a pair of normallyopen short-circuiting contacts in parallel circuit relation to saidwinding, means including a cam and cam follower for closing saidshort-circuiting contacts in response to a predetermined number ofreclosures of said main contacts, a movable supporting member, magneticmeans mounted on said supporting member for magnetically holding saidcam follower in the position occupied by said cam follower when saidshort-circuiting contacts are closed, and spring means interposedbetween said manually operable means and said supporting member formoving said magnetic means out of its holding position with respect tosaid cam follower in response to opening of said contacts by saidmanually operable means.

BENJAMIN R. HERMANN. SIDNEY R. SMITH, Jn.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 692,217 Sundh Jan. 28, 19022,069,082 Walle Jan. 26, 1937 2,414,786 Lincks et al. Jan. 2l, 1947Certificate of Correction vl'azerd: No. 2,524,525 October 3, 1950BENJAMIN R. HERMANN ET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows:

Column 3, line 3, for the Word lmmedately read immediate; column 5, line1, before occupies insert 5 column 6, line 53, for break read breaker;column 7, line 18, for preferred read performed; column 8, line 68,after arranged insert to move one of said contacts out of engagement;and that the said Letters Patent should be read as corrected above, sothat the same may conform to the record of the case in the PatentOffice.

Signed and sealed this 13th day of February, A. D. 1951.

THOMAS F. MURPHY,

Assistant Gommz'sez'oner of Patents.

Certiicate of Correction vPatent No. 2,524,525 October 3, 1950 YBENJAMIN R. HERMANN ET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows:

Column 3, line 3, for the Word immediately read immediate; column 5,line l, before occupies insert 5; column 6, line 53, for break readbreaker; column 7, line 18, for preferred read performed; column 8, line68, after arranged insert to more one of said contacts out ofengagement;

and that the said Letters Patent should be read as corrected above, sothat the same may conform to the record of the case in the PatentOffice. Signed and. sealed this 13th day of February, A. D. 1951.

THOMAS F. MURPHY,

Assistant Gommz'sez'oner of Patents.

